1. Field of the Invention
The present invention relates generally to a cascade-type multiplex radio communication relay system for relaying communication from a transmitting station to a propagation shadow area, and, more particularly, to a cascade-type multiplex radio communication relay system, in which a donor and a Main Hub Unit (MHU) are connected to each other through an Unshielded Twisted Pair (UTP) cable to enable duplex communication, and in which a plurality of remote units are connected to the MHU through UTP cables to enable duplex communication.
2. Description of the Related Art
As well known to those skilled in the art, base stations are installed at locations suitable for either communication with land mobile stations or communication based on relaying through mobile relay stations. However, high costs are required for the construction and operation of base stations. Accordingly, in locally formed propagation shadow areas which result from propagation interference or the existence of physical obstacles, such as happens in the case of the insides of buildings, subways, underground passages or tunnels, separate communication relay systems are constructed in order to relay communications for such a propagation shadow area.
A communication relay system using coaxial cables has been proposed and used as a conventional communication relay system for relaying communications of a propagation shadow area, but is disadvantageous in that coaxial cables not only are expensive but also have a low transfer rate and high transmission loss.
Therefore, as a substitute for the communication relay system using coaxial cables, a communication relay system using UTP cables has been proposed. Such a communication relay system using UTP cables is advantageous in that UTP cables are very cheap, are easily installed, and have a higher transfer rate than coaxial cables, but is disadvantageous in that, since such a UTP cable has a short transmission distance (of typically less than 100 m), the range of the application thereof is restricted, and in that there are limitations in complying with high-speed and wide-band characteristics that are required because of the development of the technology.
Accordingly, a communication relay system using optical cables has been developed. Such an optical cable is advantageous in that a large amount of data can be transmitted at high speed and the costs of the optical cable are inexpensive, but is disadvantageous in that it is not easy to handle and install the optical cable, thus making it difficult to extend a communication relay system.
Meanwhile, a radio communication relay system capable of relaying communication from a base station in a wireless manner has been developed. Such a radio communication relay system is disadvantageous in that a communication relay function is inferior to a wired communication relay system due to propagation characteristics, and requires large installation costs, but is advantageous in that, since the radio communication relay system can be freely and conveniently installed, it is very beneficial for network installations in places having complicated wire connections, such as department stores, hospitals, and museums, and places requiring temporary network connections, such as exhibition centers, seminar centers and construction sites.
However, since such a conventional radio communication relay system adopts a method of transmitting analog data, the extension of the communication relay system is limited, transmission loss is relatively high, and multiplex communication relay is difficult, and thus there occurs a problem in that the communication relay system cannot be efficiently used.